Heparin/heparin sulfate (H/HS)-like oligosaccharide (S-OligoS) were studied in vitro to elucidate their modulation of protein and cell membrane function. Understanding the molecular basis of their multifunctional biological activity could enhance their usefulness. 1) Quantitative chromatography and spectroscopy were employed to characterize structure- function relations of the heparinoid pharmaceutical SP54, a mixture of disulfated xylosyl (DiSX)-OligoS, known to inhibit infectivity of human immunodeficiency virus (HIV-1)in vitro. Sixteen size-fractionated components of SP54 showed a range of MWt. approximately -30,000 to about 1000. Two components (MWt. app 2500 and below) had low anionic density. These comprised about 45% of SP54 and exhibited low potency. Components were assayed with comparison for in vitro inhibition of killing of T4- lymphocytes by HIV-1. Dose-response relations showed a biphasic dependence of antiviral activity on MWt. app. Log EC50 (microgram DiSX/ml) was around -0.3 for components of MWt. app. 23 to appx. 5-6 KDa. EC50 rose sharply to 1.7 for MWt. app. between 5 and 2 KDa, except for a component at about MWt. 3000 (Log EC50 0.5). SP54 components are currently in comparative study of in vitro inhibition of cell fusion (syncytia formation) as well as cell killing. Significance of this study is identification of two highly active anti-HIV-1 components, one appx. a 20-mer and one an 8- or 9-mer, suggesting structural specificity as found for anticoagulantly active heparin. The bulk of SP54 has relatively low potency. 2) Components of sulfated beta-cyclodextrin were isolated to assess potential for inhibition of Kaposi sarcoma in vitro. Components exhibited differential potency; several were highly inhibitory.